1. Field of the Invention
This invention is for electro-explosive devices. In particular, this invention is for electro-explosive devices with large area uniform detonation surfaces and high safety and reliability with fast response times.
2. Description of the Prior Art
Electro-explosive devices, EEDs, fall into one of two basic groups in current technology. The first group is electro-thermally initiated devices which respond to relatively low electrical energies. The second group is electro-shock initiated devices which include exploding wire and foil designs requiring very high energy levels.
The shock initiated devices have the advantages of very fast and repeatable function times and very high resistance to inadvertent initiation. The greatest disadvantage of the second group of EEDs is the large and expensive electrical systems required to initiate them. The electro-thermally initiated group, while operating at much lower input energy requirements, have not matched the inherent input safety characteristics or response time of the shock initiated group. Typical response times for the thermally initiated group range from about 10 microseconds to several milliseconds, while the shock initiated EEDs function in less than one microsecond.
In order to obtain environmental tolerance with long shelf-life for military and aerospace systems, both types are usually designed with hermetically sealed housings. These additional requirements plus those of ensuring adequate safety in handling and system assembly require that the thermally initiated group be able to withstand reasonable unintended currents without firing. This problem does not arise in the shock initiated EED group because the currents required for firing are typically several thousand amps. However, thermally initiated designs have problems with this respect since any current will produce some heating of the bridgewire and most designs have limited capability to conduct this heat away from the thermally sensitive primary explosive. The previous approach to achieve no-fire currents above a few hundred milliamps is to use a large diameter bridgewire and thermally conductive header dielectrics. This tends to extend function time for many applications and frequently becomes the unacceptable limit. Thus, there is a need for hermetic header designs which permit high no-fire currents in combination with very fast function times for reasonable firing currents representative of traditional hot-wire EEDs. Ideally, a new device capable of no-fire currents above one amp at one watt with function times of approximately one microsecond at current levels of twenty amps is desired. None of the previous detonators in either group satisfy these requirements.